RELIABILITY OF CYBEX NORM DYNAMOMETER FOR ISOMETRIC AND ISOKONETIC TRUNK MUSCLE STRENGTH MEASUREMENTS

Abstract

The aim of this study is to investigate the reliability of Cybex Norm isokinetic dynamometer for isometric, concentric and eccentric strength measurements of the trunk flexor and extensor muscles. Eleven healthy male volunteers participated in this study. Strength measurements of the trunk muscles were performed at 30° and 60° of trunk flexion for isometric strength, at 30°/s and 180°/s angular velocities for isokinetic concentric strength, and at 30°/s and 90°/s angular velocities for isokinetic eccentric strength. To determine the inter-rater reliability, two different physicians performed the measurements with an interval of 1-2 days. To determine the intra-rater reliability, the same physician repeated the second tests following 5-7 days. Reliability was evaluated by calculating the intra-class correlation coefficient (ICC, r). The ICC’s of the isometric measurements for the trunk extensor muscles revealed high level inter- and intra-rater reliability (r=0.90-0.96). Furthermore, isokinetic concentric strength measurements of the trunk extensor muscles represented high inter- and intra-rater reliability (r=0.90-0.91) for low test speed (30°/s angular velocity), and a good inter- and intra-rater reliability (r=0.82-0.83) for high test speed (180°/s angular velocity). Additionally, isokinetic eccentric strength measurements of the trunk extensor muscles exhibited high inter-rater (r=0.95-0.96) and good intra-rater (r=0.83-0.88) reliability at both test speeds (30 and 90°/s angular velocity). On the other hand, strength measurements for the trunk flexor muscles presented high inter-rater reliability (r=0.92) for isometric strength at 30° trunk flexion and good inter- and intra-rater reliability (r=0.81-0.82) for isokinetic concentric strength at 180°/s angular velocity. This study indicated that the test protocols and dynamometer used are reliable in assessing the strength of trunk extensor muscles in isometric, isokinetic concentric and isokinetic eccentric modes in healthy individuals.